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New Telescope Time with the Planet Uranus

The two faces of Uranus as seen through the adaptive optics on the near-infrared camera of the Keck II telescope in Hawaii. The white features are high altitude clouds like Earth’s cumulous clouds, while the bright blue-green features are thinner high-altitude clouds akin to cirrus clouds. Reddish tints indicate deeper cloud layers. In each image, the north pole is at the right and is highlighted by small convective spots highly reminiscent of features seen on Saturn’s pole. Just south of the equator is a never-before-seen scalloped wave pattern similar to instabilities that develop in regions of horizontal wind shear. Image courtesy of Lawrence Sromovsky, Pat Fry, Heidi Hammel, Imke de Pater.

It’s distant, far away from Earth, but still an observational delight: the planet Uranus.

With the NASA Voyager 2 spacecraft flyby in January 1986 of the planet Uranus, those observations admittedly pictured the planet as a bland, featureless blue-green orb.

But new techniques with instruments at the Keck Observatory have shown a new face of Uranus.

The highest-resolution images ever taken of the giant ice planet in the near infrared, have revealed an incredible array of atmospheric detail and more complex weather.

Uranus is so far away — 30 times farther from the sun than Earth — that even with the best of telescopes almost no detail can be seen.

By combining multiple images of the planet taken by the Keck II telescope on the summit of Hawaii’s 14,000-foot Mauna Kea volcano, the team was able to reduce the noise and tease out weather features that are otherwise obscured. The group used two different filters over two observing nights to characterize cloud features at different altitudes.

Teasing out weather features

The planet, in fact, looks like many of the solar system’s other large planets — the gas giants Jupiter and Saturn, and the ice giant Neptune. Uranus has bands of circulating clouds, massive swirling hurricanes and an unusual swarm of convective features at its north pole.

“These images reveal an astonishing amount of complexity in Uranus’ atmosphere,” said Heidi Hammel of the Association of Universities for Research in Astronomy. “We knew the planet was active, but until now, much of the activity had been masked by the noise in the data.”

The astronomers found that in the planet’s deep atmosphere, comprised of hydrogen, helium and methane, winds blow mainly in east-west directions at speeds up to 560 miles per hour, in spite of the small amounts of energy available to drive them. Its atmosphere is the coldest in our solar system, with cloud-top temperatures in the minus 360-degree Fahrenheit range, partly due to Uranus’ great distance from the sun.

One new feature found by the group is a scalloped band of clouds just south of Uranus’ equator. The band may indicate atmospheric instability or wind shear.

“This is new, and we don’t fully understand what it means,” said Larry Sromovsky, a planetary scientist at the University of Wisconsin, Madison. “We haven’t seen it anywhere else on Uranus,” he said in a press statement.

The team of researchers reported the details of their observations Oct. 17 at a meeting of the American Astronomical Society’s Division of Planetary Sciences in Reno, Nevada.

This research was supported by grants from NASA Planetary Atmospheres and Astronomy programs, and from the Space Telescope Science Institute.

By Leonard David

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